This invention relates to editing apparatus and, more particularly, to an error detection arrangement for use in such editing apparatus.
In the field of signal recording, it often is desirable to modify or edit a recording by selectively inserting thereinto various bits and pieces which are derived from other recordings or signal sources. Video editing has become a highly specialized and advantageous art, whereby video signals which are recorded on a particular record medium, such as a magnetic tape, a magnetic disk, or the like, are edited by selectively assembling or inserting other video signals onto that record medium. For the purpose of the present discussion, the record medium on which the video signals are recorded is described as magentic tape which, presently, is the most common form of record medium that now is used for recording video programs. Typically, in the field of broadcast and commercial video tape recording, video signals which are recorded on one tape are reproduced by a video tape recorder (VTR) for an "insert" or "assemble" recording on another tape by another VTR. As is known to those of ordinary skill in the art of video editing, an "insert" edit operation describes the insertion of video signals into a predetermined location on a video tape, the " inserted" signals being preceded and followed by pre-existing video signals. In an "assemble" mode of operation, video signals are recorded in following relation (i.e. assembled) to pre-existing information.
As is recognized, to carry out the insert and assemble edit modes of operation, it is necessary for an operator to select appropriate portions, or blocks, of video signals which are to be reproduced from one tape (referred to generally as the source or playback tape) and which are to be recorded at other locations on the recording (or destination) tape. That is, the operator must be aware of the particular addresses on the source tape at which desired video signals are recorded as well as addresses on the destination tape at which new video signals are to be placed. These "addresses" on the respective video tapes generally are recorded as time code addresses, each of which separately identifies a respective frame of the recorded video signal. An example of one type of time code address which is used with, for example, the recording of NTSC signals is the so-called SMPTE (Society of Motion Picture and Television Engineers) time code which represents frame addresses in terms of hours, minutes, seconds and frames, up to a maximum value of 23 hours, 59 minutes, 59 seconds and 29 frames. Although other acceptable time code addresses are known, for convenience, and in the interest of simplification, the present discussion refers only to this SMPTE time code.
It is conventional to record the time code longitudinally, that is, in serial tracks along a length of the video tape. Time code generators and readers are known for the recording and reading of such time codes as the video tape is transported. These time codes, as read from the video tape, are used to designated so-called "edit-in" and "edit-out" locations of the respective playback and recording tapes.
To carry out an edit operation, the time code addresses which identify the particular frames on the playback tape which define the video information that is to be re-recorded on the recording tape are marked, or stored, as the edit-in and edit-out points. For an insert edit mode, the desired edit-in and edit-out points on the recording tape likewise are marked, or stored. Once an operator confirms that the material, or video signals, lying between the edit-in and edit-out points on the playback tape is correct and should be re-recorded, or transferred, between the edit-in and edit-out points on the recording tape, the actual transfer of video signals may occur. Such confirmation of this edit operation is known as a "preview", and the previewed operation may be monitored on a suitable video display monitor device. If changes are to be effected to the respective edit-in and edit-out points, for example, if the operator finds other material which he wishes to transfer from the playback tape to the recording tape, or material which should be deleted from the recording tape, the time code addresses which define the respective edit points may be suitably changed.
In some types of edit operations, it is desirable to transfer some or all of a video scene but not its accompanying audio portion. Similarly, it may be desirable to transfer only the audio portion of a recording. The result of this so-called "split" edit operation is a video recording accompanied by audio information that has been separately prepared. As an example of this, in preparing a segment for a television news broadcast, a particular newsworthy video scene may be recorded on one tape with whatever audio information accompanied that scene; and another video scene, such as that of the news commentator, may be recorded on another tape with its accompanying audio commentary. When a split-edit operation is carried out, the resultant recording may consist of the particular newsworthy video scene accompanied by the audio commentary. This split-edit procedure may be carried out by, for example, transferring the newsworthy scene to the tape on which the audio commentary is recorded or, conversely, by transferring the audio commentary to the tape on which the newsworthy scene is recorded.
As may be appreciated, it is advantageous to provide video editing apparatus with a split-edit capability such that, broadly, video signals at one location of, for example, the playback tape and audio signals at another location may be transferred to the recording tape. That is, as the playback and recording tapes are transported, the video signals commencing at point A on the playback tape, and then the audio signals commencing at point B are transferred, until point C is reached, whereat the edit operation terminates. This is referred to as a "split-in" edit operation wherein the "edit-in" locations are split between the video and audio signals. In a "split-out" operation, the points at which recording terminates are split: for example, the recording of the video signals terminates at point D and the recording of the audio signals terminates at point F. Video editing apparatus that can carry out a combined split-in and split-out operation easily, and under the control of an operator who is not necessarily highly skilled, is desirable.
In a typical video tape recording format, two audio tracks are provided upon which different audio signals may be recorded. Use of such separate aduio tracks can be turned to account in a split-edit operation by "splitting" the recording of the audio signals in these tracks. Thus, for example, in a split-in operation, recording of the video signals may commence when the playback (or recording) tape reaches point A, recording of the aduio signals in one track may commence when the tape reaches point B, and recording of the audio signals in the other track may commence when the tape reaches point C. An analogous edit-out operation likewise may be carried out. It is recognized that this offers advantageous flexibility and enhances the quality of video editing.
Many video editing devices known heretofore, if capable of performing split-edit operations, generally cannot carry out a split-out operation. Also, although separate audio tracks are provided in the typical video tape recording format, such devices do not function to "split" the recording of these audio signals. That is, the transfer, or edit, of the audio signals is accomplished simultaneously--separate edit-in or edit-out locations for such audio signals are not obtainable. A further disadvantage attending these video editing devices is a limitation on the split-in edit locations. Generally, a split-in location for the audio signals is constrained within a limited range following the video split-in location. Consequently, audio signals may not be transferrable before the video signals. Also, it may not be possible to select an audio edit-in point (such as the aforementioned point B) that is satisfactorily removed from the video edit-in point (the aforementioned point A). This may inhibit the overall capabilities and artistic results of the edit operation.
Such disadvantages are overcome by the novel editing apparatus described in copending applications Ser. No. 139,444 and Ser. No. 139,448, each filed Apr. 11, 1980. In that editing apparatus, video and audio edit-in as well as edit-out points may be selected by simple push-button operation. Common edit-in and edit-out points may be selected, respectively, for the video and audio signals or, if the operator desires, individual edit-in and edit-out points may be assigned. To assist the operator in setting up and carrying out edit operations, the editing apparatus advantageously is provided with display registers for displaying position data representing the various edit points, and with selector switches for assigning the displayed position data to those video and audio signals whose transfer is desired.
The aforedescribed editing apparatus can be operated by one who need not be a highly skilled technician. Therefore, it is desirable to provide automatic error detection to sense that the particular parameters which have been selected for the edit operation are enabling. That is, the individual edit-in and edit-out points should be checked to make sure that the edit operation can proceed as desired. For example, edit-out points should follow edit-in points, split-in and split-out points should be selected to be intermediate the start and end locations for the edit, the individual video and audio signals that are selected to be "split in" also should be "split-out", and the like. Furthermore, if an error condition is detected, appropriate indications should be produced which apprise the operator of the existence of the detected error condition, its probable location, and its probable cause. Moreover, the actual implementation of the edit operation should be inhibited in the presence of an error condition.
So far as is known, video editing apparatus having a satisfactory automatic error detection feature of the type described above is not readily available.